Funny to say but the game is too popular for their current system, way too popular. Haha.
If they want housing to be limited for feels then its fine, but I find that really silly and frustrating for multiple reasons. I think housing is a really nice element in games that all would probably enjoy to some extent (not everyone went crazy in FFXI but it was definitely a place to call your own).
Frustrating since the system is limited by itself, so its not really possible to see how many would enjoy housing or how extensive people would like features in it (say if everyone got a starter and upgrade-able plot for free, you might find that housing is a huge content for the game). Definitely could be wrong but I believe if it had a lower barrier more people would take part, and it would encourage SE to add more features and content - it would then become a better content because of it.
Of course I doubt they're just sitting on the issue because it's fun for them to watch people be frustrated. I'm sure it's some significant issue like how the architecture is set up. Or a belief that the content isn't worth that much time, "you say you want a house, but I don't believe you" lol. Personally I think players of a FF/SE game would like housing even more than other MMOs that have excellent systems just because there is a very high visual and nostalgic* element to FF games and so customization is an even bigger/better "end game" for many people, so I hope it isn't that later reason haha. *Allowing players to vaguely create some of their favorite chill spots through the series for example, a chocobo ranch, or what have you.
There are a few extra considerations to add to complicate the matter, also noting ReplicaX's comment, is that you have players who want to own multiple houses (if the system was limitless I think this would be great for the economy) and also FC that don't have a house and should probably have one due to losing out on features. Besides players owning a house per character you can effectively have multiple FC under a single account via legitimate desire and then just shell FCs for houses/to sell to people later, so there is a gray area in there as people will expand themselves to meet the demand to sell later and then also people who are not accounted for that do demand it (FCs).
664,640 houses is a lot of information to pass around though lol (#pulled from total active players on the site brought up in this thread). Perhaps a house per account, and a special memory friendly zone for FC might be able to cut that number down greatly (number of houses, amount of information being managed - it's still a lot though). Those who want another, extra, house perhaps can be put in the mogshop (I'm sure if they added enough customization besides people who want it for personal RP you'd also get people buying areas for group RP, like "inn" "restaurant" and whatever power they put into the system).